Messages in this thread | | | Date | Thu, 27 Nov 2008 15:10:54 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 2/2] tracing: identify which executable object the userspace address belongs to |
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* Török Edwin <edwintorok@gmail.com> wrote:
> On 2008-11-27 14:48, Frank Ch. Eigler wrote: > > Hi - > > > > On Thu, Nov 27, 2008 at 11:41:45AM +0100, Peter Zijlstra wrote: > > > >>>> Impact: modify+improve the userstacktrace tracing visualization feature > >>>> [...] > >>>> You'll see stack entries like: > >>>> /lib/libpthread-2.7.so[+0xd370] > >>>> [...] > >>>> > >>> Can you suggest an actual distribution & architecture where this > >>> facility may be tested/used? It appears to require frame-pointer > >>> stuff that AFAIK is not generally turned on for user-space. > >>> > >> gentoo, just rebuild world with frame pointers ;-) > >> > > > > Well, that only goes so far. If this feature turns out unable to work > > without distributors recompiling all their stuff on, for example, x86-64, > > then expectations need to be reset. > > My assumption is that this feature will be used to trace individual > applications, and not the system as a whole. Then you only need libc > to be recompiled with frame pointers on, and your own > application/your own application's libraries. > > That is what I want to use it for, and there isn't another solution > that allows me to do this. Sure I can trace userspace alone using > ptrace (which has its own overhead), and the kernel alone by using > ftrace, but I can't combine those traces in a meaningful manner. > If/when the kernel will support dwarf unwinding, it will only need > to provide an alternate implementation for save_stack_trace_user.
Yes.
> Even without frame pointers you can at least get the return address > to userspace, which may be inside your application for page faults. > > If I need to do system-wide tracing, I can use my 32-bit chroot [*], > or boot my laptop which is 32-bit. > > I don't think that this feature should get rejected just because it > is not easily usable from x86_64. > > [*] I haven't tested yet if tracing 32-bit applications from a > 64-bit kernel works. It probably won't, and I'll need to use a > different struct stack_frame with 32-bit addresses. > > Another approach I've though of would be to deliver a signal to > userspace on demand, and have the signal handler do the backtrace, > but that would unnecesary overhead.
Correct, that would be stupid.
Your patches are nice. Right now they are in tracing/core and linux-next already.
Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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